A perpendicular magnetic recording method is the method which employs a magnetic recording layer in which the easy axis of magnetization is directed perpendicular to the substrate. Compared with the longitudinal magnetic recording method, in perpendicular magnetic recording the demagnetizing field in the vicinity of the magnetization transition region, which is the boundary between recorded bits, is decreased, so that the higher the recording density, the more magnetostatically stable the recorded state, with improved resistance to thermal fluctuations; hence the method is appropriate for increasing areal densities.
In particular, when a soft magnetic underlayer, consisting of soft magnetic material, is provided between the substrate and the perpendicular magnetic recording layer, the functions of so-called perpendicular double-layer media are obtained, and excellent recording performance can be obtained. At this time, the soft magnetic underlayer serves to provide a return path for the recording magnetic field from the magnetic head, and can improve the recording and reproducing efficiency.
In perpendicular magnetic recording media, generally a soft magnetic underlayer, underlayer, perpendicular magnetic recording layer, and protective layer are formed on a substrate.
Co—Cr system alloys are widely used as the perpendicular magnetic recording material. When using Co—Cr system alloys, normally substrate heating during film deposition causes separation of the magnetic phases and nonmagnetic phases within the magnetic recording layer.
A carbon protective layer formed by a plasma CVD method is widely used as the protective layer.
In recent years, oxide magnetic materials including Co alloys (for example Co—Cr—Pt) and SiO2 or other oxides have come to be used as the material of perpendicular magnetic recording layers.
In oxide magnetic materials, a nonmagnetic phase of an oxide is segregated in such a manner as to surround the magnetic phase, of Co alloy or similar, so that the magnetic crystal grains (magnetic phase) can be isolated and made finer, and the magnetization transition region can be made smaller. As a result, media noise can be reduced (see Non-patent references 1 through 3).
Non-patent reference 1: Oikawa et al. “SiO2 composition of CoPtCr—SiO2/Ru perpendicular magnetic recording media and grain isolation”, Journal of the Applied Magnetic Society Japan, 29, 231-234 (2005).
Non-patent reference 2: Matsunuma et al, “CoCrPt alloy-oxide perpendicular magnetic recording media with a new structure incorporating an intermediate layer”, Technical Report of the Institute of Electronic, Information and Communication Engineers, MR2004-10.
Non-patent reference 3: Ohtsuki and Uwazumi “Development of perpendicular magnetic recording media for an HDD aiming at 400 Gbits/inch2”, Nikkei Electronics, Jan. 19, 2004.